Electrical safety structure

ABSTRACT

An electrical safety structure designed to prevent injury to an operator of a machine. This safety structure includes a safety circuit and an operating circuit for operating a machine when this latter circuit is closed. A pair of series-connected normally closed switches are located in the safety circuit and a pair of series-connected normally open switches are located in the control circuit and are respectively coupled with the normally open switches to form with the latter a pair of switch units spaced from each other by a distance too great to be operated by one hand of the operator. A control switch means maintains part of the operating circuit closed as long as the normally closed switches of the safety circuit remain in their closed positions and operates to enable the operator to actuate both of the switch units simultaneously to provide for simultaneous closing of both normally open switches along with simultaneous opening of both normally closed switches so that the operating circuit will be closed by the pair of series-connected normally open switches only by simultaneous actuation of both switch units and not by separate actuation of either one of the switch units. Because the operator must use both hands for simultaneous operation of the switch units, the operator&#39;&#39;s hands cannot be located at part of the machine where the operator can be injured when the machine is actuated by closing the operating circuit.

United States Patent [72] inventor Morris Weidenfeld Bayside. NY. [2]]App]. No 694,182 [22] Filed Dec. 28, 1967 [45] Patented Feb. 2, 1971[73] Assignees Morris Weidenfeld a part interest; Abraham Weidenfeld NewYork, N.Y. a part interest [54] ELECTRICAL SAFETY STRUCTURE 4 Claims, 3Drawing Figs. [52] US. Cl 317/135, 317/154 [51] Int. Cl H0lh 47/00 [50]Field of Search 317/135. 154; 192/129-131 [56] References Cited UNITEDSTATES PATENTS 3,040,399 6/1962 Rafiaelli 3l7/135X 2,369,243 2/1945Lechler 317/135 2,882,456 4/1959 Koch 317/135 Primary Examiner-Lee T.Hix Anorne vBurton Lv Lilling ABSTRACT: An electrical safety structuredesigned to prevent injury to an operator of a machine, This safetystructure includes a safety circuit and an operating circuit foroperating a machine when this latter circuit is closed. A pair ofseries-connected normally closed switches are located in the safetycircuit and a pair of series-connected normally open switches arelocated in the control circuit and are respectively coupled with thenormally open switches to form with the latter a pair of switch unitsspaced from each other by a distance too great to be operated by onehand of the operator. A controlswitch means maintains part of theoperating circuit closed as long as the normally closed switches of thesafety circuit remain in their closed positions and operates to enablethe operator to actuate both of the switch units simultaneously toprovide for simultaneous closing of both normally open switches alongwith simultaneous opening of both normally closed switches so that theoperating circuit will be closed by the pair of series-connectednormally open switches only by simultaneous actuation of both switchunits and not by separate actuation of either one of the switch units.Because the operator must use both hands for simultaneous operation ofthe switch units, the operators hands cannot be located at a part of themachine where the operator can be injured when the machine is actuatedby closing the operating circuit.

ELECTRICAL SAFETY STRUCTURE BACKGROU ND OF THE INVENTION The presentinvention relates to safety devices. In particular, the presentinvention relates to electrical safety devices to be used in connectionwith machines which are operated electrically.

As is well known, certain electrically operated machines are capable ofinjuring the operator. Such machines may include, for example, a pair ofmembers one of which moves toward the other in in order to carry out thework of the machine, and in the event that a hand of the operator islocated between these members when the work is performed by the machine,the operator can become injured.

In order to avoid this latter drawback, it has already been proposed toprovide machines of the above type with a pair of switch units to beoperated simultaneously by the operator and located from each other by adistance too great to be operated by one hand, so that the operatorshands are necessarily situated at both of the switches simultaneouslywhen the machine is actuated to carry out the required work. In this wayit was proposed to maintain the hands of the operator reliably away fromthe space between the work performing members of the machine. Thus, inthe case where work is supported by a platen and a ram drives a workingmember downwardly toward the platen to engage work thereon, with such amachine it was considered advisable to provide a safety structure of theabove type so as to maintain the hands of the operator away from thespace between the platen and the descending work performing memberactuated by the ram.

However, it has been found that in practice the desired safety is notachieved with constructions of this type. For example, certain operatorswill maintain one of the switch units of the above type in a permanentlyclosed position, as by stretching a piece of adhesive tape of the likeacross one of the switch units in a position maintaining the operatingbutton thereof depressed, so that in this way one of the switch units isalways maintained closed, and with such an expedient an operator canhave one free so that he still can become injured.

SUMMARY OF THE INVENTION It is accordingly a primary object of thepresent invention to provide a construction which will avoid the abovedrawbacks.

It is an object of the invention to provide a safety structure whichincludes a pair of switch units which must be operated simultaneously inorder for the operating circuit of a machine to be closed to actuate themachine. In other words, it is an object of the invention to provide astructure which is incapable of closing the operating circuit of themachine if one of the switch units is operated separately from the otherswitch unit.

It is furthermore an object of the present invention to provide aconstruction of this type which is exceedingly simple and fully reliablein operation.

Also, it is an object of the invention to provide a construction whichis capable of being connected to a single source of current, such asreadily available alternating current, in order to achieve the objectsof the invention.

Also, it is an object of the invention to utilize for the safetystructure readily available electrical components which are assembledtogether to provide the circuitry of the invention, so that thestructure of the invention can be provided at a relatively low cost.

Also, it is an object of the invention to provide a structure of thistype which can be readily added to existing machines, without any greateffort or cost, so as to enable such existing machines to have thesafety structure of the invention.

In accordance with the invention there is a safety circuit and anoperating circuit, the latter circuit being adapted, when closed tooperate a given machine. The safety circuit includes apair ofseries-connected normally closed switches, while the operating circuitincludes a pair of series-connected normally. open switches, and thelatter switches are respectively coupled with the normally closedswitches to form therewith a pair of switch units. Thus. when eachswitch unit is operated the normally closed switch thereof will beopened simultaneously with the closing of the normally open switchthereof. A control switch means is connected between both of thesecircuits for maintaining part of the operating circuit closed as long asthe safety circuit is closed by the series-connected normally closedswitches, and this control switch means operates with a time lagsufficiently great to enable the operator to simultaneously close bothof the normally open switches during actuation of the pair of switchunits when the normally closed switches are simultaneously opened. Theseswitch units are, of course, spaced from each other by a distance toogreat to'permit them to be operated simultaneously by one hand.Therefore, it is possible for the operator to simultaneously close thenormally open switches of the operating circuit before the controlswitch opens, and the part of the operating circuit which is closed bythe control switch means is bypassed by a bypass portion of theoperating circuit, so that when the control switch means opens aninstant after simultaneous closing of both of the normally openswitches, the operating circuit can be maintained closed.

BRIEF DESCRIPTION OF DRAWINGS The invention as illustrated by way ofexample in the accompanying drawings which form part of this applicationand in which:

FIG. 1 is a schematic representation of a machine which can becontrolled by the circuit structure of the invention.

FIG. 2 is a schematic representation of a circuit which illustrates theprinciple of the present invention.

FIG. 3 is a wiring diagram of one possible practical circuit which maybe used to operate a machine such as that schematically shown in FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to FIG. 1, there isschematically illustrated therein a machine 10 which has, for example, astationary lower platen member 12 which is adapted to carry any work onits upper surface. Situated over the platen 12 is a work member 14 whichis to be displaced downwardly toward the member 12 in order to carry outthe work of the machine 10. For example, a pair of sheets which are tobe heat-sealed to each other can be situated on the platen 12 to beexposed to pressure and heat derived from the member 14 when the latteris displaced downwardly toward the member 12. In the illustrated examplethe work member 14 is carried by a ram 16 forming part of a pistonassembly of a fluid-pressure moving means 18 which includes a cylinder20. In any suitable way this means 18, which may be pneumaticallyoperated, for example, is controlled by a solenoid-operated valve, forexample, so that when the latter valve opens upon energizing of itssolenoid air under pressure will be delivered to the cylinder 20 inorder to drive the ram 16 and the work member 14 downwardly therewith tocarry out the work of the machine.

Situated at the front of the machine, just below the platen 12, forexample, on a suitable panel 22, for example, are a pair of switch units24 and 26 which are spaced from each other by distance small enough tobe operated by two hands but too great to permit the switch units to beoperated by one hand of the operator. Between these units there is, forexample, an emergency switch 28 which can be actuated for turning offthe entire machine Also, suitable control units can be located in acontrol box 30, these control units being of a type referred to below inconnection with FIG. 3.

Thus, with this structure of FIG. 1 as long as both hands of theoperator are required for simultaneous actuation of the switch units 24and 26, the hands of the operator cannot be located between the members14 and 22 when the member 14 is driven downwardly to carry out the workwhich is to be performed by the machine 10. In this way injury to thehands of the operator is reliably avoided.

Referring now to FIG. 2, the switch units 24 and 26 are schematicallyillustrated therein. These switch units include a pair of normallyclosed third and fourth switches 32 and 34 which are located in a safetycircuit 36 which is provided with a rectifying means 38 and whichincludes a first relay coil 40 of a control switch means 42v Thenormally closed switches 32 and 34 are respectively coupled withnormally open first and second switches 44 and 46 which are connected inseries in an operating circuit 48. The normally closed switches 32 and34 are respectively coupled with the normally open switches 34 and 46 toform the pair of switch units 24 and 26, and when these units aresimultaneously operated the normally closed switches 32 and 34 will beopened while the normally open switches 44 and 46 will be closed.

The operating circuit 48 has a portion 50 which is closed by the fifthswitch 52 of the control switch means 42 as long as the relay 40 thereofis energized. When the relay 40 is not energized the normally openswitch 52 assumes its openposition opening part 50 of the operatingcircuit 48. This circuit 48 also includes a bypass portion 54 whichbypasses the part 50 of the circuit and which is closed and opened byswitch 64 of a second control switch means 60, which has a secondholding relay coil 62 connected to circuit part 50 for closing bypass 54when coil 62 is energized. The operating circuit 48 has a pair of lines56 and 58 which are adapted to be connected to any source of alternatingcurrent such as that which is available at any wall outlet and which issupplied by a public utility.

With this construction of FIG. 2, as long as the operator does notactuate the switches 24 and 26, the parts will remain in a positionshown in FIG. 2 where the operating circuit 48 is open and the safetycircuit 36 is closed although both circuits are connected to a commonsource of alternating current, the rectifying means 38 provides a directcurrent for the control switch means 42. This control switch means 42will operate with a time lag which is sufficiently great to enable theoperator without difficulty to simultaneously close the switches 44 and46 while opening the switches 32 and 34. In other words, the coil 40does not become deenergized with a speed sufficiently great to enable aspring which acts on the switch 52 to retract the latter to its openposition before the switches 44 and 46 are simultaneously closed by theoperator. When the coil 40 is energized, it maintains, the switch 52closed in opposition to the spring which maintains it in its normallyopen position. Thus, this time lag resulting from deenergizing of thecoil 40 and responding of the spring to retract the switch 52 to itsopen position is sufficiently great to provide at least that fraction ofa second which is necessary for any operator of normal coordinationcapabilities to close simultaneously both of the switches 44 and 46while simultaneously opening both of the switches 32 and 34.

As is apparent for the structure of FIG. 2, the holding relay means 60includes a coil 62 and a normally open sixth switch 64 for closing thebypass circuit portion 54. The coil 62 of the holding relay means 60cannot be energized for displacing the switch 64 to its closed positionunless both of the switches 44 and 46 are simultaneously closed with theswitch 52. The holding relay 60 is designed so that it has a smallertime lag than the control switch means 42 and thus before the switch 52becomes displaced to its open position, the energized coil 62 hasdisplaced the switch member 64 to its closed position, thus closing theswitch 64 and maintaining it closed even after the switch switch 52opens. Now current can flow through both of the switches 44 and 46 andthe bypass circuit portion 54 so that the entire operating circuit 48will remain operative while the switches 32, 34 and 52 are all open. Ifonly one of the switches 44 and 46 is closed, then the coil 62 remainsunenergized and the switch 52 opens so that if thereafter the secondswitch of the series-connected switches 44 and 46 is parent that withthis construction it is essential for the operator to simultaneouslyclose both the switches 44 and 46 in order to enable the operatingcircuit 48 to close.

.closed, the coil 62...will remain unenergized. Thus, it is ap-Referring now to FIG. 3, an actual circuit to be used with a machine isillustrated therein. The switch units 5-1 and 5-2 respectivelycorrespond to the switch units 24 and 26. The rectifier means includesthe selenium rectifier S-R, as well as a pair of resistors R-1 and R-2,and in this circuit is located the relay coil K-l which corresponds tothe coil 40. Connected across this coil K-l is an electrolytic condenserC-l, and the circuit includes an indicating lamp I-l. The lattercomponents are located in the direct current circuit portion of FIG. 3corresponding to the circuit 36 of FIG. 2.

The alternating current operating circuit which includes theseries-connected normally open switches of the units S-1 and S-2 includethe normally open switch K-la controlled by the relay coil [(-1 andcorresponding to the switch 52, and the relay coil K-2 is connected inseries with this normally open relay switch K-la. This relay coil K-2corresponds to the coil 62 of FIG. 2 and controls the switch K-2a whichis normally open, this latter switch becoming closed only uponenergizing of the coil [(-2 when both of the series connected normallyopen switches of the units S-1 and 5-2 are closed, as was describedabove in connection with the embodiment of FIG. 2.

With the particular construction shown in FIG. 3, the closing of theswitch K-2a by energizing of the holding relay coil [(-2 uponsimultaneously closing of both of the normally open switches of theoperating circuit will result in energizing of the third solenoid valveor relay S.V. connected in series with the switch K-2a, so that in thisway the machine 10 of FIG, 1 will be actuated.

In the illustrated example, the energizing of the coil K-2 also servesto close a second normally open relay switch K-2b which serves throughnormally closed switch K-3b to actuate a timer T-2, which 52 a delaytimer relay having coil T-2 and normally closed switch T-2a. It will benoted that once this switch K-2b is closed, the circuit will remaincomplete for a period of time determined by the timer T-2 even if theswitches S-1 and S-2 are released by the operator, so that in this waythe heat sealing operations, for example, will be carried out. Theswitch K-3b controlled by the relay coil K-3 is normally closed andopens when the relay coil K-3 is energized, so that this switch does notopen until expiration of the time determined by the timer T-2. In thisway, a certain delay will be achieved by the coil T-2 and the heatsealing timer T-l becomes energized upon closing the switch S-4 so thatthis timer T-l will provide a heat sealing operation of predeterminedduration. There is also connected into the circuit suitable resistorsR-3 and R4 as well as counter C and various indicating lamps such as thelamp [-1 in the rectifier circuit and the lamp 1-2 in the delay circuit.

Thus, with the direct current relay K-l and the alternating currentrelays K-2 and K-3, it is possible with a circuit as described above, tobring about the desired operations in connection with heat-sealing ofsheets to each other, for example, and at the same time the hands of theoperator are reliable maintained from the space between the workingcomponents of the machine. FIG. 3 also shows at the lower left, thenormally closed switch S-3 corresponding to the switch 28 and capable ofbeing opened at any time by the operator in order to open the completecircuit and prevent the operations from continuing, so that this switch8-3 is an emergency switch which is normally closed but which can beopened whenever desired in order to terminate the operation of thernachine.

Controls of this type referred to above in connection with FIG. 3 arehoused within the control box 30 indicated schematically in FIG. 1.

Thus, it will be seen that by way of the simple structure describedabove and having the features of FIG. 2, it is possible to control anymachine, such as that of the type shown in FIGS. 1 and 3, and thissafety structure of FIG. 2 can be easily added to any existing machineat relatively low cost.

lelaim:

1. An electrical apparatus, a safety assembly comprising and operatingcircuit and a safety circuit, said operating circuit having a first andsecond series-connected normally open switches and said safety circuithaving a third and fourth series-connected normally closed switchesrespectively coupled with said first and second normally open switchesto form a pair of switch units to be manually actuated by opening saidnon'nally closed switches simultaneously with the closing of saidnormally open switches. one side of said first switch connected to oneside of a third switch and to one side of a source of alternatingcurrent said switch units being spaced apart from each other by adistance small enough to be operated by two hands but too great to beoperated by one hand of the operator, one side of a first relay coilconnected to one side of said fourth switch, the other side of saidfirst relay coil connected to the other side of said source ofalternating current, a fifth switch controlled by said first relay coilin a closed position when said first relay coil is energized, said fifthswitch connected to one side of said second switch and to one side of asecond relay coil and to one side of a third coil, the second side ofsaid second relay coil and the third coil being connected to said otherside of said source of said alternating current, a sixth switch, saidsecond relay coil controlling said sixth switch, said first relay coilwhen deenergized operating to open said fifth switch with a time lagsufficiently great to enable the operator to simultaneously close bothof said normally open switches and open both of said normally closedswitches to close said sixth switch by means of a current passingthrough said second relay coil. said operating circuit having a bypasscircuit portion which includes said sixth switch connected in parallelwith said fifth switch. said bypass circuit portion being energized whensaid time lag lapses, said third coil controlling said electricalapparatus and being directly energized when said second relay coil isenergized.

2. The combination of claim 1 and wherein said safety circuit is adirect current circuit while said operating circuit is an alternatingcurrent circuit.

3. The combination of claim 1 and wherein the electrical apparatusincludes a machine and in said operating circuit a plurality ofelectrically operable control units for controlling said machine so thatthe latter cannot be operated unless both said switch units aresimultaneously actuated by the operator.

4. The combination of claim 3 and wherein the machine has a moving meansand a pair of members one of which is movable by said moving meanstoward the other for carrying out the work of the machine, said membersdefining between themselves a space beyond which the operator must keephis hands in order not to be injured, and one of said control unitsbeing operatively connected with said moving means to actuate the latterwhen said one control unit is energized.

1. An electrical apparatus, a safety assembly comprising and operatingcircuit and a safety circuit, said operating circuit having a first andsecond series-connected normally open switches and said safety circuithaving a third and fourth seriesconnected normally closed switchesrespectively coupled with said first and second normally open switchesto form a pair of switch units to be manually actuated by opening saidnormally closed switches simultaneously with the closing of saidnormally open switches, one side of said first switch connected to oneside of a third switch and to one side of a source of alternatingcurrent, said switch units being spaced apart from each other by adistance small enough to be operated by two hands but too great to beoperated by one hand of the operator, one side of a first relay coilconnected to one side of said fourth switch, the other side of saidfirst relay coil connected to the other side of said source ofalternating current, a fifth switch controlled by said first relay coilin a closed position when said first relay coil is energized, said fifthswitch connected to one side of said second switch and to one side of asecond relay coil and to one side of a third coil, the second side ofsaid second relay coil and the third coil being connected to said otherside of said source of said alternating current, a sixth switch, sAidsecond relay coil controlling said sixth switch, said first relay coilwhen deenergized operating to open said fifth switch with a time lagsufficiently great to enable the operator to simultaneously close bothof said normally open switches and open both of said normally closedswitches to close said sixth switch by means of a current passingthrough said second relay coil, said operating circuit having a bypasscircuit portion which includes said sixth switch connected in parallelwith said fifth switch, said bypass circuit portion being energized whensaid time lag lapses, said third coil controlling said electricalapparatus and being directly energized when said second relay coil isenergized.
 2. The combination of claim 1 and wherein said safety circuitis a direct current circuit while said operating circuit is analternating current circuit.
 3. The combination of claim 1 and whereinthe electrical apparatus includes a machine and in said operatingcircuit a plurality of electrically operable control units forcontrolling said machine so that the latter cannot be operated unlessboth said switch units are simultaneously actuated by the operator. 4.The combination of claim 3 and wherein the machine has a moving meansand a pair of members one of which is movable by said moving meanstoward the other for carrying out the work of the machine, said membersdefining between themselves a space beyond which the operator must keephis hands in order not to be injured, and one of said control unitsbeing operatively connected with said moving means to actuate the latterwhen said one control unit is energized.